1. Field of the Invention
The present invention relates to a ring laser, and more particularly to a gyro apparatus for detecting rotation utilizing a semiconductor laser, in particular a gyro apparatus capable of detecting the rotating direction, and a driving method and a signal processing method therefor.
2. Related Background Art
As the gyro apparatus for detecting the angular velocity of rotation, there are already known a mechanical gyro having a rotor or an oscillator, and an optical gyro. Particularly the optical gyro is causing a revolution in the field of gyro technology, since it can be activated instantly and has a wide dynamic range.
Within such-optical gyro, there are known a ring laser gyro, an optical fiber gyro, a passive ring resonator gyro etc. The ring laser gyro utilizing a gas laser is already commercially employed in the airplanes or the like.
Also as a compact ring laser gyro of high precision, there is proposed a gyro based on a semiconductor ring laser formed on a semiconductor substrate, as disclosed in the Japanese Patent Publication No. 62-39836, the Japanese Patent Application Laid-open No. 4-174317 and the Japanese Patent Publication No. 6-38529.
The gyro based on the semiconductor ring laser enables reduction in the device size, in the electric power consumption and in the start-up time in comparison with the mechanical gyro having an oscillator, and is therefore suitable for use as an antivibration control device for preventing the error in phototaking by hand vibration in a still camera and a video camera.
In such a gyro, the beat frequency contains the information of angular velocity. For detecting the beat frequency, there are a method of converting the beat frequency into a voltage signal by a frequency-voltage conversion circuit, and a method of directly detecting the beat frequency by a frequency counter.
However, the conventional ring laser gyro is incapable of detecting the rotating direction by its output signal. Therefore the rotating direction is detected by applying a small rotational vibration (dither) and utilizing the correlation between such dither and the signal.
Also the Japanese Patent Publication No. 62-39836 and the Japanese,Patent Application Laid-open No. 4-174317 do not suggest the specific method for detecting the rotating direction.
In consideration of the foregoing, an object of the present invention is to provide an optical gyro capable of detecting the angular velocity and the rotating direction with sufficient accuracy.
Another object of the present invention is to provide a driving method for the optical gyro, capable of suppressing the variation in the beat frequency at the standstill state.
(1) At first a case of employing two ring lasers will be explained.
The optical gyro of the present invention is provided with ring lasers and detection means for detecting the beat frequency of the ring lasers, wherein there are a first ring laser which increases the beat frequency when the angular velocity increases to a certain direction from the standstill state, and a second ring laser which increases the beat frequency when the angular velocity increases regardless of the rotating direction, and such first and second ring lasers are positioned so as to be optically independent of each other.
In a such configuration, the beat frequencies of the two ring lasers correspond to the frequencies of the variations in the impedances of the respective ring lasers, and such changes in the frequencies corresponding to the variations of the impedances have respectively different dependences on the angular velocity. It is therefore possible to obtain the angular velocity by signal processing of such changes. In the following, a more detailed description will be given on a configuration employing a semiconductor ring laser as the ring laser.
In the semiconductor ring laser, the relationship between the angular velocity and the signal frequency becomes non-linear or the signal cannot be obtain, in a certain angular velocity range, though such situation depends on the shape of the wave guide path to a certain extent.
By employing the two semiconductor ring lasers of mutually different angular velocity dependence, with different angular velocity ranges of such non-linearity, it is possible to obtain the signals from the two semiconductor ring lasers and to execute signal processing by employing either of the signals or combining the signals. Such process allows to obtain the angular velocity without being influenced by the non-linearity.
Also in the first semiconductor ring laser, the frequency change corresponding to the variation in the impedance is not symmetrical with respect to the rotating direction (sign of the angular velocity), and this fact can be utilized for detecting the rotating direction.
Also by executing addition or subtraction with suitable weighting on the frequency changes corresponding to the variations in the impedances in the two semiconductor ring lasers, the beat frequency in the first semiconductor ring laser in the standstill state can be obtained. Therefore, that it is possible to execute feedback control to suppress the variation in beat frequency in the stand still state. Also, it is possible to reflect the variation in the beat frequency in the standstill state on the single processing for obtaining the angular velocity.
Consequently, a gyro, in which precisely measures the angular velocity and the rotating direction, can be constructed from such two semiconductor ring lasers.
Also the signal processing method for the optical gyro of the present invention is featured in that the angular velocity is detected from the signal of the first ring laser when the absolute value of the angular velocity is smaller than a predetermined value, and the absolute value of the angular velocity is obtained from the signal of the second ring laser when the absolute value of the angular velocity is larger than the predetermined value.
Also the signal processing method for the optical gyro of the present invention is featured in that, in a prespecified first angular velocity range, the signal from the first ring laser and the signal from the second ring laser are processed to determine the beat frequency of the standstill state, and, in a second angular velocity range, the angular velocity is obtained from the aforementioned beat frequency of the standstill state,and the signal from the first semiconductor ring laser.
It is further featured in that the angular velocity ranges are determined from the result of processing of the signal from the first ring laser and the signal from the second ring laser, and the method of signal processing is switched according to such ranges.
Furthermore, the signal processing method for the optical gyro of the present invention is featured in that the signal from the first ring laser and the signal from the second ring laser are processed and the rotating direction is detected from the result of such processing.
Also the driving method for the optical gyro of the present invention is featured in that the signal from the first ring laser and the signal from the second ring laser are processed to determine a value corresponding to the beat frequency at the standstill state, and feedback control is executed so as to stabilize such a beat frequency.
Furthermore, the optical gyro of the present invention is featured in that a first ring laser having a tapered area asymmetrical to the optical wave guide and a second ring laser not having an asymmetrical tapered area are positioned so as to be optically independent.
(2) In the following a case of employing three ring lasers will be explained.
The optical gyro of the present invention is provided with mutually optically independent three or more semiconductor ring lasers, including at least a pair of the semiconductor ring lasers showing mutually opposite changes in the frequency of the variation in the impedance with respect to the rotation in a direction, and a ring laser in which the beat frequency at the standstill state is zero.
The optical gyro of the present invention is provided with three or more semiconductor ring lasers each of which shows a change in the frequency of the variation in the impedance between terminals according to the applied angular velocity and is provided with electrical terminals for detecting such variation in the impedance and which are provided on mutually non-perpendicular planes so as to be mutually optically independent, and which include a first semiconductor ring laser showing a decrease in the frequency of the variation in the impedance when the angular velocity increases in a direction, a second semiconductor ring laser showing an increase in the frequency of the variation in the impedance when the frequency of the variation in the impedance of the first semiconductor ring laser decreases, and a third semiconductor ring laser showing an increase in the frequency of the variation in the impedance when the absolute value of the angular velocity increases.
In the above-descibed configuration, since the semiconductor ring lasers are mutually independent optically, the frequency of the variation in the impedance of the first and second semiconductor ring lasers becomes higher in one of these semiconductor lasers and lower in the other, when the optical gyro is rotated in whichever direction. Also in the third semiconductor ring laser, the frequency of the variation in the impedance is proportional to the absolute value of the angular velocity of the rotation except for an area with smaller angular velocity in which the lock-in is large.
Therefore, in a range with a small angular velocity, the signals indicating the changes in the frequencies of the impedance variations in the first and second semiconductor ring lasers are processed. Between the semiconductor ring lasers, it is possible to separate a noise which shows changes of the same sign and a signal which dependents on the angular velocity and shows changes of different signs. Therefore, the signal-to-noise ratio is improved, and the angular velocity is precisely obtained, including the sign indicating the rotating direction. Also in the third semiconductor ring laser, in a range of large angular velocity, which is free from the lock-in, the angular velocity can be precisely obtained from the change in the frequency of the impedance variation in the third semiconductor ring laser. Such angular velocity can be obtained with a high precision since it is not influenced by the fluctuations in the frequency of the impedance variation in the standstill state. Also, even in such an angular velocity range, it is possible to process the changes in the frequencies of the impedance variations in the first and second semiconductor ring lasers thereby separating an angular velocity-dependent signal showing changes of different signs between these semiconductor lasers, and determining the rotating direction from the sign of such signal.
Also in the optical gyro of the present invention, each of the first and second semiconductor ring lasers has laser lights which propagate in the mutually opposite directions in the respective optical resonator and have different oscillation frequencies at the standstill state, wherein the relationship of magnitude of the oscillation frequencies of the laser light propagating clockwise and that propagating counterclockwise is inverted between the aforementioned two lasers, while, in the third semiconductor ring laser, the laser lights propagating in the mutually opposite directions in the optical resonator have the same oscillation so that frequency at the standstill state.
In the above-described configuration, in each of the first and second semiconductor ring lasers, the two laser lights propagating in the mutually opposite directions in the respective optical resonator and having different oscillation frequencies at the standstill state generate an optical beat within the optical resonator. Also, since the first and second semiconductor ring lasers are mutually independent optically, the oscillation frequencies of these laser lights change independently when the optical gyro equipped with such semiconductor lasers is rotated. As the relationship of magnitude of the oscillation frequencies of the clockwise propagating laser light and the counterclockwise propagating laser light is inverted between the two semiconductor ring lasers, the frequency of the optical beat in the optical resonator increases in one of the semiconductor lasers while that in the other decreases when the gyro is rotated.
In the third semiconductor ring laser, when the angular velocity of rotation is large and is free from lock-in, the oscillation frequencies of the clockwise propagating laser light and the counterclockwise propagating laser light change independently to generat an optical beat in the optical resonator. The frequency of such optical beat is proportional to the absolute value of the angular velocity. The change in the frequency of the optical beat in the first to third semiconductor ring lasers can be detected as a change in the frequency of the impedance variation between the terminals.
Therefore, in a range of small angular velocity, the changes in the frequencies of the impedance variations in the first and second semiconductor ring lasers are processed. Between the semiconductor ring lasers, it is possible to separate a noise which shows changes of same sign and a signal which is dependent on the angular velocity and shows changes of different signs. Therefore, the signal-to-noise ratio is improved and precise angular velocity is obtained, including the sign indicating the rotating direction. Also in the third semiconductor ring laser, in a range where the angular velocity is large and free from lock-in, the angular velocity can be obtained precisely from the change in the frequency of the impedance variation in the third semiconductor ring laser. Such angular velocity can be obtained with a high precision since it is not influenced by the change in the frequency of the impedance variation in the standstill state. Also, even in such angular velocity range, it is possible to process the changes in the frequencies of the impedance variations in the first and second semiconductor ring lasers to separate an angular velocity-dependent signal showing changes of different signs between these semiconductor lasers, and to determine the rotating direction from the sign of such signal.
The optical gyro of the present invention is featured in that each of the first and second semiconductor ring lasers is provided, in a part of the optical wave guide, with a tapered portion consisting of a first portion in which the width of the optical wave guide gradually increases in the propagating direction of the clockwise laser light and a second portion in which the width of the optical wave guide gradually decreases, that the first portion is longer than the second portion in the first semiconductor ring laser while the second portion is longer than the first portion in the second semiconductor ring laser, and that the third semiconductor ring laser is not provided with such tapered portion.
In the above-described configuration, the tapered portions in the first and second semiconductor ring lasers are introduced in order to provide a difference between the oscillation frequencies of the clockwise laser light and the counterclockwise laser light in the standstill state. In addition, the relationship of the lengths of the first and second portions of the above-mentioned tapered portion is inverted between the first and second semiconductor ring lasers. Therefore the dependence of the resonator loss on the propagating direction becomes mutually opposite between the first and second semiconductor ring lasers, so that the magnitude relationship between the oscillation frequencies of the clockwise laser light and the counterclockwise laser light becomes inverted between the first and second semiconductor ring lasers.
The aforementioned tapered portion functions in more details in the following manner. The laser light propagates in the optical resonator, repeating total reflection at the interface of the optical wave guide. In the aforementioned tapered portion, there is a loss because the angle of incidence upon the interface of the optical wave guide becomes deviated from the total reflecting condition. As the angle of incidence upon the interface of the tapered portion is different depending on the propagating direction, a difference in the loss is generated, so that the resonator loss depends on the propagating direction. The difference in the losss results in a difference in the oscillation threshold of the ring laser. Therefore, when two laser lights of opposite propagating directions simultaneously oscillate in the samiconductor ring laser with the tapared portion, a difference in the density of the photons is produced. Such difference in the photon density leads to a difference in the oscillation frequency of the ring laser by a non-linear effect.
Also in the above-described configuration, since the third semiconductor ring laser is not provided with the tapered portion, the resonator loss has no dependence on the propagating direction, so that the oscillation frequency of the clockwise laser light coincides with that of the counterclockwise laser light in the standstill state.
In the first and second semiconductor ring lasers, the two laser lights propagating in the mutually opposite direction in the respective optical resonator and having different oscillation frequencies at the standstill state generate an optical beat in the optical resonator. Also, since the first and second semiconductor ring lasers are mutually independent optically, the oscillation frequencies of the laser lights vary independently when the gyro equipped with such semiconductor lasers is rotated. Since the magnitude relationship of the oscillation frequencies of the clockwise laser light and the counterclockwise laser light is inverted between the two semiconductor ring lasers, the frequency of the optical beat increases in one of the optical resonators and decreases in the other when the gyro is rotated.
Also in the third semiconductor ring laser, when it has a large angular velocity of rotation and is free from the lock-in, the oscillation frequencies of the clockwise laser light and the counterclockwise laser light vary independently to generate an optical beat in the optical resonator. The frequency of such optical beat is proportional to the absolute value of the angular velocity. The change in the frequency of the optical beat in any of the first to third semiconductor ring lasers can be detected as a change in the frequency of the impedance variation between the terminals.
Therefore, within a range where the angular velocity is small, signal processing is executed on the changes in the frequency of the impedance variation in the first and second semiconductor ring lasers. Between these semiconductor ring lasers, it is possible to separate a noise showing changes of the same sign and dependent signal angular velocity showing changes of different signs, thereby improving the signal-to-noise ratio and precisely obtaining the angular velocity, including the sign indicating the rotating direction. Also in the third semiconductor ring laser, in a range where the angular velocity is large and is not influenced by lock-in, the angular velocity can be obtained from the change in the frequency of the impedance variation in the third semiconductor ring laser. Such angular velocity is of a high precision, since it it not influenced by the change in the frequency of the impedance variation in the standstill state. Also in such angular velocity range, the changes in the frequencies of the impedance variations in the first and second semiconductor ring laser can be processed to obtain an angular velocity-dependent signal showing the changes in opposite directions between these semiconductor lasers, and the rotating direction can be judged from the sign of such signal.
Also in the optical gyro of the present invention, the ratio of the area surrounded by the optical resonator to the circumferential length thereof is the same in the first and second semiconductor ring lasers.
In the above-described configuration, the ratio of the area surrounded by the optical resonator to the circumferential length thereof is a parameter determining the absolute value of the change in the beat frequency with respect to the change in the angular velocity. If this parameter is the same in the two semiconductor ring lasers, the amount of the aforementioned change in the beat frequency is the same in the absolute value and is different in the sign. It is therefore further facilitated to separate the angular velocity-dependent signal showing changes of different signs between the semiconductor ring lasers, from the noise or the change in the beat frequency in the standstill state, showing changes of same sign, whereby the signal-to-noise ratio can be improved. As a result, the angular velocity and the rotating direction can be known in more precise manner from the angular velocity-dependent signal.
Also in the optical gyro of the present invention, the shapes of the optical resonators of the first and second semiconductor ring lasers are mutually in a mirror symmetry relationship. In the above-described configuration, since the shapes of the optical resonators of the first and second semiconductor ring lasers are mutually in a mirror symmetry relationship, the dependence of the resonator loss on the propagating direction also becomes mirror symmetric between the two semiconductor ring lasers. More specifically, the propagating loss of the clockwise laser light in the first semiconductor ring laser becomes equal to that of the counterclockwise laser light in the second semiconductor ring laser, and same applies to other laser lights. Therefore, if the driving condition is the same in the two semiconductor ring lasers, the beat frequencies mutually coincide at the standstill state. In the relationship between the angular velocity and the frequency of impedance variation, such beat frequency at the standstill state is a component not dependent on the angular velocity. If this value is the same in the two semiconductor ring lasers, it becomes possible to highly precisely separate a signal component dependent on the angular velocity by a subtracting operation on the signals from the two semiconductor ring lasers. The signal-to-noise ratio can be improved since the noise component not dependent on the angular velocity can also be suppressed by the subtracting operation. As a result, the angular velocity and the rotating direction can be known in precise manner.
Also in the optical gyro of the present invention, the ratio of the area surrounded by the optical resonator to the circumferential length thereof is the same between at least either of the first and second semiconductor ring lasers and the third semiconductor ring laser.
In the above-described configuration, the ratio of the area surrounded by the optical resonator to the circumferential length thereof in at least either of the first and second semiconductor ring lasers and in the third semiconductor ring laser is a parameter determining the absolute value of the change in the beat frequency with respect to the change in the angular velocity. If this parameter is the same in the two semiconductor ring lasers, the amount of the aforementioned change in the beat frequency is the same at least in the absolute value. Therefore, if the angular velocity of the rotation of the gyro is larger than the angular velocity affected by the lock-in in the third semiconductor ring laser, the frequency of the optical beat proportional to the absolute value of the angular velocity in the third semiconductor ring laser and the amount of change of the beat frequency from the standstill state in at least either of the first and second semiconductor ring lasers become mutually equal in the absolute value. Hence, it is possible to precisely separate the beat frequency at the standstill state and to control the driving condition for the semiconductor ring laser in such a manner that such beat frequency is stabilized in time. Also in separating the angular velocity dependent signal, it is possible to reduce the fluctuations of the signal in time, thereby improving the precision of separation.
The driving method for the optical gyro of the present invention is featured in that each of the aforementioned plural semiconductor ring lasers is driven under a constant current, and a change in voltage is detected from the aforementioned electrical terminals.
Also the driving method for the optical gyro of the present invention is featured in that each of the aforementioned plural semiconductor ring lasers is driven under a constant voltage, and a change in the driving current. is detected from the aforementioned electrical terminals.
In the above-described configurations, the constant voltage,or current drive allows to obtain the variation in the impedance of the device by a simple circuitry, and also allows easy connection to various signal processing circuits. Also in the signal processing circuit, it is possible to separate an angular velocity dependent signal showing changes of different signs between the first and second semiconductor ring lasers from a noise or a variation in the beat frequency in the standstill state, showing changes of the same sign, thereby improving the signal-to-noise ratio. It is also rendered possible to switch the signal processing method according to the angular velocity, and to precisely obtain the angular velocity from the signal of the third semiconductor ring laser when the angular velocity is large. In this manner, the angular velocity and the rotating direction can be precisely known within a wide angular velocity range.
Also in the driving method for the optical gyro of the present invention, the injection current or the applied voltage is the same in the first and second semiconductor ring lasers.
In the above-described configuration, the same injected current or the same applied voltage reduces the difference in the oscillation frequencies, the light intensities, and the heat generations in the first and second semiconductor ring lasers and brings about the coincidence of the oscillation frequencies in the standstill state, and is particularly useful when the shapes of the resonators of the two semiconductor ring lasers are in mirror symmetry. Such driving mode realizes the beat frequency in the standstill state, which constitutes a component not dependent on the angular velocity and a component corresponding to the frequency of impedance variation, which is common to the first and second semiconductor ring lasers. It is therefore rendered possible to easily and precisely separate the signal component dependent on the angular velocity from the noise and the component of the beat frequency not dependent on the angular velocity, thereby improving the signal-to-noise ratio. As a result, the angular velocity and the rotating direction can be known precisely from the angular velocity dependent signal.
The signal processing method for the optical gyro of the present invention is also featured in selecting specified one or multiple ones from the plural semiconductor ring lasers and obtaining the angular velocity from the signals, which are extended from selected semiconductor ring laser(s).
In the above-described configuration, by selecting the first and second semiconductor ring lasers, the variations in the beat frequency corresponding to the angular velocity in a range of small angular velocity can be obtained, and such variations can be processed to obtain the rotating direction and the angular velocity with an improve signal-to-noise ratio. Also in a range with large angular velocity and without influence of the lock-in, the beat frequency proportional to the absolute value of the angular velocity can be obtained from the third semiconductor ring laser, whereby the angular velocity can be obtained with high precision. It is therefore rendered possible to obtain an angular velocity signal of high precision and little influence of noise by selecting the devices and executing signal processing according to the angular velocity. It is also possible to improve the response speed of the gyro by selecting a device showing a high frequency of impedance variation and utilizing the signal from such device for processing.
The signal processing method for the optical gyro of the present invention is also featured in obtaining the angular velocity only from the signals of the first and second semiconductor ring lasers when the absolute value of the angular velocity is smaller than a predetermined value.
In the above-described configuration, in the first and second semiconductor ring lasers, the frequencies of the impedance variations change according to the angular velocity because of the absence of lock-in even when the absolute value of the angular velocity is smaller than the predetermined value. It is therefore possible to obtain the rotating direction and the angular velocity by processing such changes.
More specifically, when the optical gyro is rotated in whichever direction, one of the frequencies of the impedance variations in the first and second semiconductor ring lasers decreases while the other increases. By signal processing on these frequencies, it is thus possible to separate an angular velocity dependent signal showing changes of different signs in these semiconductor lasers from the noise showing changes of the same sign, thereby improving the signal-to-noise ratio and precisely obtainig the angular velocity including the sign indicating the rotating direction.
The signal processing method for the optical gyro of the present invention is also featured by arithmetically processing the frequencies of the impedance variations in the first and second semiconductor ring lasers thereby obtaining the angular velocity and the rotating direction.
In the above-described configuration, the arithmetic processing in the frequencies of the impedance variations in the first and second semiconductor ring lasers is to separate an angular velocity-dependent signal and the beat frequency at the standstill state which is not dependent on the angular velocity.
In such operation, angular velocity-dependent signal showing changes of opposite signs between the two semiconductor ring lasers is separated from the noise and the variation in the beat frequency at the standstill state showing changes of the same sign, whereby the signal-to-noise ratio can be improved. As a result, the angular velocity and the rotating direction can be known with even better precision from the angular velocity dependent signal.
The signal processing method for the optical gyro of the present invention is further featured in that the aforementioned arithmetic processing is a subtraction or a weighted averaging with a negative weighting.
In the above-described configuration, the difference in the frequencies of the impedance variations, which is obtained by the subtraction, is proportional to the angular velocity, including the sign indicating the rotating direction. Such configuration is particularly useful when if the first and second semiconductor ring lasers are under the same driving condition, and show approximately the same beat frequencies at the standstill state and the variations in the beat frequencies with respect to a change in the angular velocity are same in the absolute values but different in the sign.
Also the weighted averaging with negative weighting allows to cancel out a signal component resulting from the beat frequency at the standstill state, which is not dependent on the angular velocity, thereby a signal proportional to the angular velocity including the sign indicating the rotating direction is obtained. Such processing is beneficial when the two semiconductor ring lasers have different beat frequencies at the standstill state. The weighted averaging can be achieved by obtaining the reciprocals of the frequencies of the impedance variations of the two semiconductor ring lasers at the standstill state, and multiplying one of the reciprocals by (xe2x88x921) as the weights.
In this operation, the angular velocity-dependent signal showing changes of different signs between the semiconductor ring lasers can be separated from the noise and the variation in the beat frequency at the standstill state showing changes of the same sign, whereby the signal-to-noise ratio can be improved. As a result, the angular velocity and the rotating direction can be measured with further improved precision, from the angular velocity dependent signal.
The signal processing method for the optical gyro of the present invention is further featured in executing an arithmetic processing on the frequency of the impedance variation in the third semiconductor ring laser, thereby obtaining the absolute value of the angular velocity.
The signal processing method for the optical gyro of the present invention is further featured in comparing the frequency of the impedance variation in at least either of the first and second semiconductor ring lasers with a reference frequency, thereby obtaining the rotating direction.
The signal processing method for the optical gyro of the present invention is further featured in executing an arithmetic processing on the frequency of the impedance variation in the first and second semiconductor ring lasers, thereby obtaining the rotating direction.
The signal processing method for the optical gyro of the present invention is further featured in that the arithmetic processing is a subtraction or a weighted averaging with negative weighting.
In the above-described configurations, if the angular velocity is larger than a predetermined value and is free from the lock-in, the third semiconductor ring laser does not have the beat frequency at the standstill state and generates a frequency of the impedance variation proportional to the absolute value of the angular velocity without being influenced by the variation in the beat frequency, whereby the absolute value of the angular velocity can be known precisely. In a such state, the rotating direction can be measured by comparing the frequency of the impedance variation between the terminal with a reference frequency in at least either of the first and second semiconductor ring lasers. Otherwise, the rotating direction can be obtain by comparing the frequencies of the impedance variation between the terminals of the first and second semiconductor ring lasers. It is therefore possible to obtain the angular velocity and the rotating direction with high precision, without being influenced by the beat frequency at the standstill state.
A driving method for the optical gyro of the present invention is featured in switching the method for controlling the driving condition, according to the value of the angular velocity signal obtained from the optical gyro.
In the above-described configuration, the aforementioned control of the driving condition is to stabilize the beat frequencies generated in the first and second semiconductor ring lasers in the standstill state, thereby improving the precision of separation from the beat frequency in the standstill state not dependent on the angular velocity. In this manner the angular velocity can be precisely determined from the angular velocity-dependent signal.
More specifically, in a range with a large angular velocity, the third semiconductor ring laser shows linearity to the angular velocity and does not have the beat frequency at the standstill state, so that it is free from the variation of such beat frequency. Therefore, in the range of a large angular velocity, the frequency of the impedance variation obtained in the third semiconductor ring laser is utilized for separating the beat frequencies at the standstill state in the first and second semiconductor ring lasers, thereby achieving control to stabilize such beat frequencies. In the range where the angular velocity is small, the frequencies of the impedance variations obtained only from the first and second semiconductor ring lasers are adopted to separate the beat frequencies of the first and second semiconductor ring lasers in the standstill ate, whereby executed is such control as to stabilize such beat frequencies.
The driving method for the optical gyro of the present invention is further featured, when the absolute value of the angular velocity is smaller than a predetermined value, by executing an arithmetic processing on the frequencies of the impedance variation in the first and second semiconductor ring lasers, and controlling the driving condition utilizing the result of such processing.
In the above-described configuration, the above-mentioned arithmetic processing is to separate a component not dependent on the angular velocity, based on the impedance variations between the terminals of the first and second semiconductor ring lasers. The above-mentioned control of the driving condition is to stabilize in time the component not dependent on the angular velocity, and such stabilization allows to improve the precision of separation of the signal component dependent on the angular velocity. In this manner, the angular velocity can be measured precisely from the angular velocity dependent signal.
The driving method for the optical gyro of the present invention is further featured in that the aforementioned arithmetic calculation is an addition or a weighted averaging.
In the above-described configuration, the addition or the weighted averaging is to separate a component not dependent on the angular velocity from the frequency signals, which indicate the impedance variations and are obtained from the first and second semiconductor ring lasers. By controlling the driving condition so as to stabilize in time the component not dependent on the angular velocity, it is possible to improve the precision of separation of the component dependent on the, angular velocity, and the angular velocity can be obtained precisely from the angular velocity dependent signal.
Particularly if, in the first and second semiconductor ring lasers, the amounts of change in the frequencies of the impedance variations with respect to the change in the angular velocity are mutually the same in the absolute value but different in the sign, the component not dependent on the angular velocity can be obtained by addition. Also if, in the first and second semiconductor ring lasers, the amounts of change in the frequencies of the impedance variations with respect to the change in the angular velocity are not mutually equal, it is possible to differentiate the absolute values of the amounts of change with respect to the angular velocity and adopt the reciprocals of the results of differentiation as the weights in the weighted averaging.
The driving method for the optical gyro of the present invention is further featured in, when the absolute value of the angular velocity is larger than a predetermined amount, taking the angular velocity obtained from the third semiconductor ring laser as a reference and controlling the drive condtion in such a manner that the angular velocity obtained from the first and second semiconductor ring lasers coincides with the above-mentioned reference angular velocity.
In the above-described configuration, the third semiconductor ring laser shows linearity to the angular velocity in the range of large angular velocity and does not have the beat frequency at the standstill state, thereby being free from the influence of the variation of the beat frequency and thus providing a high precision. Therefore, the angular velocity obtained from the third semiconductor ring laser is taken as the reference for control. The angular velocity can also be obtained from the first and second semiconductor ring lasers because of the changes in the frequencies of impedance variations according to the angular velocity, but is influenced by a change in the beat frequency at the standstill state. The control of the driving condition so as to bring the latter angular velocity to the reference value corresponds to suppressing the variation in the beat frequency at the standstill state.
Such a control of the driving condition to stabilize the beat frequency at the standstill state improves the precision of separation of the signal component dependent on the angular velocity, and the angular velocity can be precisely obtained from such an angular velocity-dependent signal.
The driving method for the optical gyro of the present invention is further featured by interrupting the drive for one of parts of or all of plural semiconductor ring lasers when the angular velocity is within a first predetermined angular velocity range and re-starting the drive when the angular velocity comes out of a second predetermined angular velocity range.
In the above-described configuration, when the angular velocity is within the first angular velocity range, the drive of a semiconductor ring laser, which does note effect the aforementioned signal processing, is interrupted to reduce the electric power consumption. When the angular velocity comes out of the second angular velocity range, the drive of such semiconductor ring laser is re-started and the signal obtained therefrom is also used in the aforementioned signal processing for detecting the angular velocity.
The driving method for the optical gyro of the present invention is further featured by interrupting the drive for the third semiconductor ring laser when the absolute value of the angular velocity is smaller than a first predetermined value and re-starting the drive when the absolute value of the angular velocity is larger than a second predetermined value.
In the above-described configuration, since the third semiconductor ring laser is influenced by the lock-in in the low angular velocity range, it is not used for the signal processing and the drive therefor is interrupted to reduce the electric power consumption when the absolute value of the angular velocity is smaller the first predetermined value. When the angular velocity becomes larger than the second predetermined value, the drive for the third semiconductor ring laser is re-started and the signal obtained therefrom is also used in the aforementioned signal processing for detecting the angular velocity.
The driving method for the optical gyro of the present invention is further featured in that the first angular velocity range is different from the second angular velocity range.
The driving method for the optical gyro of the present invention is further featured in that the first angular velocity range is included in the second angular velocity range.
In the above-described configuration, the angular velocity at which the drive of the semiconductor ring laser is interrupted is different from the angular velocity at which the drive is re-started, thereby realizing a hysteresis on the angular velocity and avoiding frequent on/off operations of the drive, which is caused by a small change in the angular velocity.